Induction furnace



` `lian. l0, 1928.

1,655,983 P. H. BRACE INDUCTION FURNME Filed April 2. 1927 WITNESSES:

y AT'TORNEY D determined self-regulating with respect to temperature.

Patented Jan. l0,` 1928..

-UNITED STATES PATENT oprima.`

ronTnn. n. nnACn: or WILxINsnURC, PENNSYLVANIA, AssIeNon To wEsTING-HoUsE ELECTRIC a MANUFACTURING COMPANY, A CORPORATION or IEN'NSYI.`

Application iiled April 2,

My invention relates lto electric furnaces and more'particularly tofurnaces of the induction type.

Y An yobjectof my invention is the provisionv of an induction furnacefor meltiig metallic material of relatively low electrical resistivityand low melting point which is operative on alternating current atcommercial frequency, that is, of the order of 60 cycles.

Another object'of my invention is the pro- Vision, in a substantiallycylindricaly induced, with means whereby heat generated in the core istransmitted to the charge and to adjacent furnace parts.

Another object of my inventionn is the provision of an induction furnacehaving precharacteristics In the inductive melting Qi @als of a;resistivity and low `melting point, such as aluminum, copper, zinc andtheirl alloys, it

has beencustomarycto employ either highfrequency furnaces, orlow-frequencyl ironcore furnaces.

Furnaces of the'high-frequency type are objectionable because ofthespecial generat- 0 ing equipment required for the 500-5000 cycle supply,andfurnaces of the low-frequency iron-core -type'are objectionablebecause the molten' metal is confined to a relatively narrow Ychannel,vand the iron cores must be laminated and artiiicially cooled.

By my invention, I propose to employ a Crucible to maintain the melt insubstantially cylindrical form having a partial ironcore which isunlaminated and'uncooled, so that o the heat generated'thereinsubstantially as-l sistsin the melting operation, and, where thediameter of the melt exceeds approximately seven inches, the inductorcoil may be energized by alternating current at '55 cycles. c

In practicing my invention, I employ an.

induction furnace comprising a primary or inductor coil, a -`cruciblecontaining a metallic charge surrounded by said coil and a rela- 50tively short solid core of magnetic material' extending a short distanceinto said Crucible and co-axi al therewith, whereby upon theenergization of said coil, a flux is set upthrough INDUCTION rUnNAcn.

192i'.v serial No. 180,454;

said cor/aand said metallic charge, andthe.

heat generated in the core is transmitted to the ehargelto materiallyassist in 'the vmelting peration.

In the drawing,

Figure 1 is a view, in vertical section, ,of

van induction furnace embodying my invention, and

Fig. 2 is a view, in vertical section, of a modifiedA form of myinvention. 4

The furnace, as shown in Fig. 1, comprises a substantially cylindricalcontainer or casing 1 formed of suit-able material, refractory in thepresent instance, a helically wound inductor coil 2 withinisaid casing,anda crucible 4 of non-conducting refractory material within said/coil 2and coaxial withsaid coil' and casing. The crucible, coil and casing aremaintained in spacedoperativerelation by a quantity ofjloose refractorymaterial 3, such, for example, as Zircon sand.

The inductor coil 2 is tubular to permit thel passage of cooling fluidtherethrough; the connections for conducting the fluid into, and awayfrom, the 'coil 'not being shown. Suitable electrical connections, alsonot 'l shown, are provided tocoiinect the coil with a source ofcommercial-frequency alternat-A ing current to effect the energizationthereof.

A removable refractory cover 5 fortlie furnace is provided with a block6 of ferromagnetic material secured to the under/side thereof by meansof'a plate 7 formedaintegral/with said block at one end thereof andimbedded iny said cover, the,l arrangement be! ing Such that, with thecover in operative position, the block 6 depends therefrom a substantialdistance ,into said Crucible and constitutes a partial fcore for coil 2.A cap 8 of insulating refractory material covers7 the biock 6 to preventcontact of the melttherwith.

A passage 9 is formedin the upper face of thefuriiaoe to extend from theCrucible 4 to the casing 1 and terminating in a spout 10, forfacilitating discharge of molten material from .said Crucible.

The device in Fig. 2 is substantially/the with. A suitable cover .ofrefractory ma is provided.'

fperature of the melt. As soon, however, as

. rious 'terial, not shown), similar to that shown in Fig. 1 ut withoutthe depending core 6, 7,

The operation of furnaces of the two types shown is substantially thesame. The inductor coil 2 is energized by connecting it to analternating-current line, having a frequency ofthe order of 60 cycles,which sets up an electromagnetic iux through the iron core and thecharge, constituting the secondary of the coil. The core serves toincrease the ,electromagnetic,coupling between the coil and the charge,and, being unlaminated and notl articially cooled, considerablehysteresis and eddy current eat is generated therein. The'heatf sogenerated is conducted, to a large extent, to the metallic material tobe melted and, to some extent, to the adjacent parts of the furnacewhich'norma'l/ly run too cool for eiicient operation.

Heat is also generated in the metallic vcharge by thei passage of .the'flux therethrough, the diameter of the charge being such that thecurrent is concentrated at the peripher thereof, because of the wellknown skin e'ct, and the heat generated thereby is conductedinwardlytobthe center of the charge where the density is practically nil.

Assuming constant current in coil 2, as the -Itemperature of coil 6rises there isa decrease in the' magnetization thereof which continuesto decrease, responsive to a rising temperature, to a point where thecore is completely demagnetized. The decrease in magnetization of thecore'causes a consequent ecrease in the magnetic couplingbetween thecore and the melt .which tends to'reduce the temthe temperature of themelt decreases appreciably, the temperature of the core will decrease,and an increase of the magnetizationl ofthe core will result which willagain raise the temperature of the melt. The temperature at which thisself regulation takes place is dependent vupon the temperature coecientof magnetization of the core, so that by the utilization of metals oralloys of vapredetermined temperature coeiicients of magnetization,automatic regulation at any desired temperature may be obtained.

'While thestructure described is intended 'short distance therein;-

.will'depend, to a large degree, upon the physical and chemicalcharacteristics ofithe material to be melted but I contemplate the useof relatively lovv frequencies, as employed in industrial installations,with a possible upper limit of 180 cycles. Y

By my invention, metals and alloys of rel-1L atively low' electricalresistivity, and low melting point, may be efficiently inductivelyheated and melted with standard electrical generating equipment, whichobviates the necessity of the 10 to 25 cycle generators for the usualring-type of iron-core indue` tion furnace, and the 500 to 500Q.cyclegenerators for the usual high-frequency furnaces'; and, since heatgenerated in the core is toassist in the melting operation, it isunnecessary to laminate said core or to provide means forartiliciallycooling the same.

In addition, by selecting cores of the proper temperature coeiicient ofmagnetization,

the attainable temperature in the charge may y ,bel redetermined andmaintained automatica gy. u

Various modications and chan es may be made without departing from t espirit and scope ofthe invention, and I desire, therefore, that onlysuch limitations shall be placed thereon as are' imposed by the prior'art or set forth in the appendedclaims.

I claim as my invention:

1. In an induction furnace, an induction crucible containing ametalliccharge melted, a partial core in' lon tudinal alinement withsaidcrucible an' projecting a and a primary coil coaxial with, andsurrounding, -said crucible and core.

4. In an induction furnace, a rimary inductor coil, a crucible surrouned by said primarily for use in melting metals-and alcoil and containingmetallic material to be loys of lou7 electrical resistance and lowmeltinelted, a solid core of magnetic. material ing point, it isconsidered within the scope also surrounded by said coil, and meansperof myl invention to make necessary alteramitting a /ortion of saidcore to project intoy tions-thereim dependingy upon the nature'ofsaidcruci le so that said core 1s the material to be melted.' 'For example,if electromagnetically coupled with said metalthe furnace is to be usedlin melting magnetic lic material. material, lamination of the 'corewould ob- 5. In an induction furnace, an inductor y yiously'have to beresorted to,/as it would coil energized at commercial-frequency, al-

55' otherwise too hot. ,l

ternating current, a Crucible surrounded by Throughout thetspecicatin, Ihave resaid coil and/'containing a metallic charge, a 1.0

i solid core of magnetic material also surrounded by said coil and meansforming a part of said crucible for ermitting` said core to be partiallysurrounded by said charge but out of actual contact therewith, so thatheat enerated in said core is conducted to said c arge to assist in theheating thereof.

6. In an induction furnace, a cylindrical crucible containing anon-'ferrous metallic char e, an inductor coil surrounding said crucile, a solid core of ferro-magnetic material within said coil, adepression in the base of said crucible for recelving a portion of saidcore therein so that a portion of said charge surrounds a portion ofsaid core, and means for energizing said inductor coil /by alternatingcurrent at commercial frequency.

7. In an induction furnace.7 thefcombination with a crucible containinga metallic charge and an inductor coil surrounding said cruel le, ofmeans for causin a self-regulation of the temperature of sald charge,comprising a solid ferro-magnetic core possessing a predetermined`Vtemperature magnetization coecient and so positioned within said coilthat a portion thereof projects into said metallic charge.

In testimony whereof, I have hereunto subscribed my 1927.

.PORTER H. BRACE.

name this 28th day of March, l0

